How do I apply a procedural generated scratch overlay across multiple mesh
Using Geometry Node's Position socket you are able to mark surfaces from a global coordinates perspective.  Simply add an overly once you have a desired pattern generating.  Here is an EXAGERATED example just to show what happens.  Kepping in mind all the boards have exactly the identical material applied. Eliminating the need to apply image textures.


Of course the final scratching will be much more refined and detailed. :)